Neutrino Anomalies & CEνNS

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Amy Morton
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1 Neutrino Anomalies & CEνNS André de Gouvêa University PIRE Workshop, COFI February 6 7, 2017

2 Something Funny Happened on the Way to the 21st Century ν Flavor Oscillations Neutrino oscillation experiments have revealed that neutrinos change flavor after propagating a finite distance. The rate of change depends on the neutrino energy E ν and the baseline L. The evidence is overwhelming. ν µ ν τ and ν µ ν τ atmospheric and accelerator experiments; ν e ν µ,τ solar experiments; ν e ν other reactor experiments; ν µ ν other and ν µ ν other atmospheric and accelerator expts; ν µ ν e accelerator experiments. The simplest and only satisfactory explanation of all this data is that neutrinos have distinct masses, and mix.

3 A Realistic, Reasonable, and Simple Paradigm: ν e ν µ = U e1 U e2 U e3 U µ1 U µ2 U µ3 ν 1 ν 2 ν τ U τ1 U eτ2 U τ3 ν 3 Definition of neutrino mass eigenstates (who are ν 1, ν 2, ν 3?): m 2 1 < m 2 2 m 2 2 m 2 1 m 2 3 m 2 1,2 m 2 13 < 0 Inverted Mass Hierarchy m 2 13 > 0 Normal Mass Hierarchy tan 2 θ 12 U e2 2 U e1 2 ; tan 2 θ 23 U µ3 2 U τ3 2 ; U e3 sin θ 13 e iδ [For a detailed discussion see e.g. AdG, Jenkins, PRD78, (2008)]

4 The Three-Flavor Paradigm Fits All Data Really Well [ modulo short-baseline anomalies LATER] [A. Marrone, Talk at Neutrino 2016]

5 Understanding Neutrino Oscillations: Are We There Yet? [NO!] (m 3 ) 2 (m 2 ) 2 What is the ν e component of ν 3? (θ 13 0!) (m 1 ) 2 ( m 2 ) sol Is CP-invariance violated in neutrino oscillations? (δ 0, π?) [ yes hint] ( m 2 ) atm ν e Is ν 3 mostly ν µ or ν τ? [θ 23 π/4 hint] ν µ ν τ ( m 2 ) atm What is the neutrino mass hierarchy? ( m 2 13 > 0?) [NH weak hint] ( m 2 ) sol (m 2 ) 2 (m 1 ) 2 (m 3 ) 2 All of the above can only be addressed with new neutrino normal hierarchy inverted hierarchy oscillation experiments Ultimate Goal: Not Measure Parameters but Test the Formalism (Over-Constrain Parameter Space)

6 ν e ν µ = U e1 U e2 U e3 U µ1 U µ2 U µ3 ν 1 ν 2 ν τ U τ1 U τ2 U τ3 ν 3 What we have really measured (very roughly): Two mass-squared differences, at several percent level many probes; U e2 2 solar data; U µ2 2 + U τ2 2 solar data; U e2 2 U e1 2 KamLAND; U µ3 2 (1 U µ3 2 ) atmospheric data, K2K, MINOS; U e3 2 (1 U e3 2 ) Double Chooz, Daya Bay, RENO; U e3 2 U µ3 2 (upper bound evidence) MINOS, T2K. We still have a ways to go!

7 What Could We run Into? New neutrino states. In this case, the 3 3 mixing matrix would not be unitary. New neutrino matter interactions. These lead to, for example, new matter effects. If we don t take these into account, there is no reason for the three-flavor interpretations of oscillation data to close. Weird stuff. CPT-violation. Decoherence effects (aka violations of Quantum Mechanics. ) etc. I will come back to some of these.

8 Not all is well: The Short Baseline Anomalies Different data sets, sensitive to L/E values small enough that the known oscillation frequencies do not have time to operate, point to unexpected neutrino behavior. These include ν µ ν e appearance LSND, MiniBooNE; ν e ν other disappearance radioactive sources; ν e ν other disappearance reactor experiments. None are entirely convincing, either individually or combined. However, there may be something very very interesting going on here...

9 LSND MB ν MB, ν [Courtesy of G. Mills]

10 [Statistical Errors Only] [Courtesy of G. Mills]

12 What is Going on Here? Are these anomalies related? Is this neutrino oscillations, other new physics, or something else? Are these related to the origin of neutrino masses and lepton mixing? How do clear this up definitively? Need new clever experiments, of the short-baseline type! Observable wish list: ν µ disappearance (and antineutrino); ν e disappearance (and antineutrino); ν µ ν e appearance; ν µ,e ν τ appearance.

13 A neutrino oscillation solution require new neutrino states ν 4, ν 5, etc with masses m 4, m 5, etc. Reason is simple: L/E too small (hence Short Baseline Anomalies). ν e ν µ ν τ ν s1. = U e1 U e2 U e3 U e4 U µ1 U µ2 U µ3 U µ4 U τ1 U τ2 U τ3 U τ4 U s1 1 U s1 2 U s1 3 U s ν 1 ν 2 ν 3 ν 4. The probability that ν 4 is measured as a ν e is U e4, the probability that ν 5 is measured as a ν µ is U µ5, and so on. [Parameterizing the matrix is interesting. E.g., AdG, Jenkins, PRD78, (2008)]

14 ( m 2 ) atm ν e ( m 2 ) LSND ν µ ν τ ( m 2 ) LSND ν s ( m 2 ) atm ( m 2 ) sol ( m 2 ) sol 2+2 requires large sterile effects in either solar or atmospheric oscillations, not observed

15 J. Kopp et al, arxiv:

16 Bottom line: Fits to all data are mediocre no feel good solution! On the other hand, I think it is not correct to say the hypothesis is ruled out. New in 2016 Data on ν µ disappearance from MINOS and Ice Cube, combined with data on ν e from Daya Bay did not make matters better. J. Kopp et al, arxiv:

17 [sin 2 2θ αα = 4 U α4 2 (1 U α4 2 ) sin 2 2θ eµ = 4 U e4 2 U µ4 2 ] [Giunti, arxiv: ]

18 Near Future Expectations Lots of Activity [C. Giunti, arxiv: ]

19 If the oscillation interpretation of the short-baseline anomalies turns out to be correct... We would have found new particle(s)!!!!!! [cannot overemphasize this!] Lots of Questions! What is it? Who ordered that? Is it related to the origin of neutrino masses? Is it related to dark matter? Lots of Work to do! Discovery, beyond reasonable doubt, will be followed by a panacea of new oscillation experiments. If, for example, there were one extra neutrino state the 4 4 mixing matrix would require three more mixing angles and three more CP-odd phases. Incredibly challenging. For example, two of the three CP-odd parameters, to zeroth order, can only be seen in tau-appearance.

20 For example, if the new neutrino states are the right-handed neutrinos from the standard seesaw, independent from the short-baseline anomalies (for an inverted mass hierarchy, m 4 = 1 ev( m 5 ))... [AdG, Huang, ] ν e disappearance with an associated effective mixing angle sin 2 2ϑ ee > An interesting new proposal to closely expose the Daya Bay detectors to a strong β-emitting source would be sensitive to sin 2 2ϑ ee > 0.04; ν µ disappearance with an associated effective mixing angle sin 2 2ϑ µµ > 0.07, very close to the most recent MINOS lower bound; ν µ ν e transitions with an associated effective mixing angle sin 2 ϑ eµ > ; ν µ ν τ transitions with an associated effective mixing angle sin 2 ϑ µτ > A ν µ ν τ appearance search sensitive to probabilities larger than 0.1% for a mass-squared difference of 1 ev 2 would definitively rule out m 4 = 1 ev if the neutrino mass hierarchy is inverted.

21 Coherent Elastic Neutrino Nucleus Scattering (CEνNs) This is the elastic, neutral current process: To date, it has never been observed. ν α N ν α N In the Standard Model, it is flavor independent. Furthermore, if the momentum transfer is small, enough, the process is coherent; instead of talking to individual quarks or individual nucleons, the neutrinos interact with the entire nucleus: σ A 2. F (q 2 ) is the form factor (known well enough). In the coherent limit, q 2 0, F (q 2 ) 1.

22 Physics capabilities will depend on the source and the ability of the detector to see very low-energy nuclear recoils. [Lindner et al, ]

23 [Kosmas et al, arxiv: ]

24 CEνNS and a fourth neutrino Since CEνNs is a neutral current process, it is the wrong place to look for one neutrino flavor converting into another neutrino flavor. ν e and ν µ look the same! However, it is the only place where you can see the non-standard model flavor, since it interacts with matter in a different way. For example, sterile neutrinos do not interact at all.

25 [Dutta et al, arxiv: ]

26 [dru differential rate unit, related to background (events/kg/day/kev)] [Dutta et al, arxiv: ]

27 CEνNS and New Neutrino Interactions New neutrino matter interactions can also be probed in CEνNS. For example, new neutral-current-like interactions (NSI) can be parameterized in the usual way

28 [Lindner et al, arxiv: ]

29 CEνNS and neutrino electromagnetic properties Nonzero neutrino masses imply that neutrinos have a nonzero electromagnetic moment, i.e., the couple to photons. L µ αβ ν α σ µν ν β F µν + d αβ ν α σ µν ν β Fµν If the neutrinos are Majorana fermions, µ αβ = µ βα (same for d) so only the transition moments are not zero. This is irrelevant for the discussion here! For CEνES, which adds incoherently to the SM expectation. µ eff is a combination of the appropriate µ αβ and d αβ.

30 The best laboratory bounds are from ν + e elastic scattering and it is very difficult to compete!

31 [Kosmas et al, arxiv: ]

32 CEνNS but NOT neutrinos: dark photons and dark matter There is a lot of work on very light dark matter and accompanying very light, new gauge bosons (ALP s, dark photons, dark Z s etc). Examples, from deniverville et all, arxiv: : or (kinetic mixing) (gauged baryon number) Idea is dark matter production (e.g., π 0 γv ( ) γ + χ + χ) followed by χ + N coherent elastic scattering.

33 [deniverville et all, arxiv: ]

34 Parting Words The venerable Standard Model sprung a leak in the end of the last century: neutrinos are not massless! [and we are still trying to patch it... ] 1. We still know very little about the new physics uncovered by neutrino oscillations. In particular, the new physics (broadly defined) can live almost anywhere between sub-ev scales and the GUT scale. 2. Neutrino masses are very small we don t know why, but we think it means something important. 3. Neutrino mixing is weird we don t know why, but we think it means something important. 4. What is going on with the short-baseline anomalies? 5. CEνNs provides a unique way to test the short-baseline anomalies. If they are confirmed, CEνNs provide a great tool to see then sterile neutrinos. 6. CEνNs also provide information on the existence of new gauge bosons (Z s or dark photons), neutrino electromagnetic properties, and new neutrino interactions.

Overview of Reactor Neutrino

Overview of Reactor Neutrino Chan-Fai (Steven) Wong, Wei Wang Sun Yat-Sen University 22 September 2016 The 14th International Workshop on Tau Lepton Physics Many thanks to Jia Jie Ling, Liang Jian Wen